The gastrointestinal microbiome influences physiological functions and is altered in a variety of diseases. The causality of "dysbiosis" in the pathogenesis is not always proven; association studies are often involved. Patients with IBD, bacteria, fungi, bacteriophages, and archaea show disease-typical patterns associated with metabolome disturbances. Fecal microbiome transfer (FMT) for treating various diseases is the subject of numerous clinical studies. Currently, recurrent Clostridioides difficile infection (rCDI) is the only confirmed indication recommended in medical guidelines. In Germany, the FMT is subject to the Medicines Act and may only be carried out as part of individual healing attempts or clinical studies. For patient safety, repeated donor screening, ideally with the construction of a chair bench, is necessary. This significantly limits the nationwide availability of the FMT in Germany. Microbiota-based therapeutics prepared from the stool of tested donors have recently been approved by the US Food and Drug Administration (FDA) for the prevention of rCDI. More microbiome-based medicines can be expected in the future.